For producing fermented foods and drinks such as shochu, koji molds which are a kind of filamentous fungi have been used. The koji molds are cultured by the solid culture method, in which koji molds are allowed to grow on surface of cereals, that is, referred to as solid koji method. The method employing solid koji is a traditional production method. However, the method is a specific culture mode, that is, solid culture, so unsuitable for large-scale production.
On the other hand, the liquid koji, which is culture product of koji molds obtained by liquid culturing koji molds, can control culture easily, and suitable culture method for efficient production. However, it has been widely known that the liquid koji does not provide sufficient enzymatic activity required for producing fermented foods and drinks such as shochu brewing (see, Non-patent Documents 1 to 4). Therefore, there are few examples of the liquid koji being used in actual production.
In production of enzymes by liquid culturing filamentous fungi comprising koji molds, it has been known that the enzymatic productivity is improved by controlling low the concentration of nutrients such as glucose in culture system. Conventionally, the concentration of nutrients such as a saccharide has been suppressed by the feeding culture method in which nutrients such as saccharide are added little by little from outside of the culture system. However, a simpler procedure has been expected to be developed (see, Non-patent Documents 5 to 6).
We have developed a method of producing koji mold culture product containing sufficient amounts of enzymes such as glucoamylase and acid-stable α-amylase, by culturing koji molds using liquid medium in which the raw material is covered with husks or hulls, and have already filed patent applications (see, specifications of Japanese Patent Application Nos. 2004-350661, 2004-352320, 2004-352324, 2004-378453, 2005-290651, and 2005-290648). However, a mechanism how to produce the enzymes in high yields in the production method, a method how to adjust enzymatic productivity in koji mold culture product based on the mechanism, and a method how to adjust enzymatic productivity of filamentous fungi except koji molds have not been known.
On the other hand, there has been proposed a method of liquefying unboiled and unsteamed starch by using the enzyme liquid obtained by culturing, in liquid medium containing unboiled and unsteamed raw material, minerals and the like, a novel strain of genus Corticium which has extremely high ability of saccharifying the unboiled and unsteamed starch (see, Patent Document 1). There has also been proposed a method of producing Sake, in which the above-mentioned enzyme liquid to react with the unboiled and unsteamed raw material (see, Patent Document 2). However, the genus Corticium is one of bacidiomycetes, so it is significantly various from the koji molds which are widely used for producing fermented foods and drinks. In addition, Patent Document 1 and Patent Document 2 describe that a black koji mold (Aspergillus awamori) and genus Rhizopus are insufficient in saccharification abilities. It is still unclear whether the enzyme liquid has sufficient acid-stable α-amylase activity.
Non-patent Document 1: Hata Y. et. al.: J. Ferment. Bioeng., 84, 532-537 (1997)
Non-patent Document 2: Hata Y. et. al.: Gene., 207, 127-134 (1998)
Non-patent Document 3: Ishida H. et. al.: J. Ferment. Bioeng., 86, 301-307 (1998)
Non-patent Document 4: Ishida H. et. al.: Curr. Genet., 37, 373-379 (2000)
Non-patent Document 5: Bhargava S. et. al.: Biotechnol Bioeng., 82(1), 111-7 (2003)
Non-patent Document 6: Pedersen H. et. al.: Appl Microbiol Biotechnol., 53(3): 272-7 (2000)
Patent Document 1: JP H05-068237 B
Patent Document 2: JP H06-053059 B